High expectations have been placed on the development of nonaqueous secondary batteries including a lithium-ion secondary battery because they can produce a high voltage and have a high capacity. In addition to Li (lithium) and Li alloys, natural or artificial graphite (graphite carbon materials) into/from which Li ions can be intercalated/deintercalated have been used for negative electrode materials (negative electrode active materials) for nonaqueous secondary batteries.
Recently, however, a further increase in the capacity is demanded of batteries for compact and multifunctional portable devices. For this reason, materials capable of holding Li as much as possible, such as low crystalline carbon, Si (silicon) and Sn (tin), are receiving attention as negative electrode active materials (hereinafter also referred to as “high capacity negative electrode materials”).
As one of such high capacity negative electrode materials for nonaqueous secondary batteries, SiOx, which has a structure in which Si ultrafine particles are dispersed in SiO2, is receiving attention (e.g., Patent documents 1 to 3). When this material is used as a negative electrode active material, charging/discharging can be performed smoothly because Si reactive with Li is in the form of ultrafine particles. At the same time, since SiOx particles themselves having the aforementioned structure have a small surface area, the material can provide favorable coating properties when they are used to form a coating for forming a negative electrode mixture layer as well as favorable bonding between the negative electrode mixture layer and the current collector.